Users of combustible and non-combustible tobacco products can be very sensitive to the taste of the product they use. The processes involved in manufacturing such products can result in removal of constituents of the tobacco which contribute to taste and/or aroma. As a result, it can be desirable to enhance the flavour of the tobacco before, during or after processing.
Further to this, it can be desirable to create products which provide the user with a taste or aroma sensation associated with a tobacco product, but which do not themselves contain tobacco, for example, tobacco-free or nicotine-replacement products.
It can also be desirable to create products which provide the user with a particular taste or aroma sensation, for example, a menthol flavour and/or smell.
These objects can be achieved by the use of flavourants and/or aroma agents.
Flavourants are substances which are capable of imparting a sensation in the mouth of the user. The sensation is perceived principally by the senses of taste and smell, but can also be detected by the tactile and heat receptors in the mouth, which detect trigeminal sensations such as astringency, pungency and heat/cooling.
Most substances which produce flavours in the mouth are polar, non-volatile and water soluble. Substances which impart an aroma must be sufficiently volatile to allow detection within the olfactory receptors, either via the nasal or oral passageways. The multitude of flavours that a user is able to detect arise from interactions of chemical compounds with taste, trigeminal and aroma receptors.
Some examples of non-volatile and volatile aroma and flavourant compound classes are provided in Table 1 below, however, it must be appreciated that chemicals of a single class can elicit many diverse flavours, especially at different concentrations.
TABLE 1Compound ClassSensory CharacterExampleAldehydesFruityHexanal, pentanal, acetaldehyde,vanillinAlcoholsSweetMenthol, maltol,EstersBitterEthyl acetate, ethyl butyrateKetonesCaramelDiacetyl, ionone furanonesPhenolicsMedicinal, smokeyPhenol(s), guaiacols
Agents which have flavourant and/or aroma properties can be derived from various sources. Many of these sources are natural, for example cellulosic materials such as Mentha arvensis or Mentha piperita, from which a mint flavourant may be isolated, Zingiber officinale, from which a ginger flavourant can be isolated, the buds of Ribes nigrum (blackcurrant), from which the flavourant solanone can be isolated, Trigonella foenum-graecum (fenugreek), from which the flavourant dihydroactinidiolide can be isolated, and Cichorium intybus, from which a chicory flavourant can be isolated.
Another source of flavourants is tobacco, which is known to contain flavourants such as pulegone; piperonal; geranylacetone; 3-methylbutanal; benzene ethanol; methyl tetradecanoate; aromatic aldehydes such as benzaldehyde and phenyl acetaldehyde; alkyl aldehydes such as nonanal, pentanal and hexanal; alkenylbenzenes such as safrole, trans-anethole, myristicin and methyleugenol; ketones such as ionone, solanone; terpene alcohols such as linalool; and monocyclic or volatine terpenes such as cembrene and dihydroactinidiolide.
It is desirable to be able to extract constituents which may have flavourant and/or aroma properties from cellulosic material.
It is possible to extract components of cellulosic material using solvents. For example, CN 1166 753 discloses the use of petroleum ether and absolute ethanol, applied under hot or cold conditions to extract components from tobacco, thereby providing a “tobacco extractum”. However, this method of extraction has the disadvantage that it requires a processing step to separate and remove the solvent from the extract, for example a filtration or distillation step. The need for an additional processing step to remove the solvent is time-consuming and costly, and can also result in removal of constituents of the cellulosic material which have similar physical properties to the solvent from the “extractum”. For example, an extracted aromatic or flavour compound which has a similar boiling point to the solvent may be removed with the solvent as a result of separation by distillation, which distinguishes between components on the basis of boiling point. This can result in contamination of the solvent with the extracted aromatic or flavour compound, and loss of the flavour/aroma compound from the extract. It is also known that soluble components of cellulosic material can be extracted using solvents in the supercritical state. This process is known as supercritical extraction, or supercritical fluid extraction.
A supercritical fluid is any substance at a temperature or pressure above its thermodynamic critical point. When a fluid is close to its critical point, small changes in pressure or temperature result in large changes in properties such as density.
The basic principle of supercritical fluid extraction is that a feed material is contacted with a supercritical fluid, resulting in the partitioning of volatile substances within the feed material into the supercritical phase. After dissolution of any soluble material, the supercritical fluid containing the dissolved substances is removed, and the dissolved components of the feed matter are separated out from the supercritical fluid.
As used herein, “supercritical fluid” refers to a medium at a temperature and pressure at or above its critical point, preferably above its critical point. As temperature and pressure are increased along the liquid/gas phase line, the distinction between the liquid and gaseous states gradually disappears to a point, the so called “critical point”, where the liquid and gaseous phases become one phase. Hence, supercritical fluids are characterised by physical and thermal properties that are between those of the pure liquid and gas. Accordingly, the expression “supercritical fluid” encompasses a medium having two phases when pressure and/or temperature are below and near the critical point and a medium with only one phase when pressure and temperature is at or above the critical point. Near and above the critical point the properties of the medium change rapidly with only slight variations of pressure and/or temperature. Supercritical fluids have solvating powers similar to liquid organic solvents, but have much higher diffusivities, lower viscosities and lower surface tensions and therefore readily penetrate porous and fibrous solids. The solvating power of supercritical fluids can, as a consequence, be adjusted by changing the pressure or temperature.
WO 01/65954 discloses a method comprising the use of a supercritical fluid extraction medium at elevated temperature and pressure, to treat tobacco in order to remove nitrosamines.
CN 1899142 discloses the use of supercritical CO2 to remove the nicotine content from tobacco leaves.
Supercritical extraction has the advantage over other extraction techniques that the solvent can be removed from the extract without the need for an additional processing step. The system can be returned to atmospheric (or non-supercritical) conditions following extraction, thereby resulting in evaporation of the solvent. This has the advantage that the solvent in pure form (i.e. without being contaminated by extracted components) can be collected and recycled within the system, whilst none of the extracted constituents are lost to the solvent.
Supercritical extraction does not allow, however, for the selective removal of individual components from the feed material. If, therefore, it is desirable to remove a particular component(s) from the feed material, the desired component must be isolated from the supercritical fluid, and the remaining substances re-circulated back to the feed material.
For example, supercritical extraction can be carried out under conditions sufficient to extract essentially all solutes from cellulosic feed matter. Extraction is then followed by an isolation step, wherein the constituent components are separated from the supercritical fluid. An isolated component may be removed, whilst the other components are recycled with the supercritical fluid to the cellulosic feed matter, thereby effectively reconstituting the feed matter.
An example of this procedure is provided by EP 0 280 817, which discloses a process which aims to provide tobacco with reduced levels of nicotine, whilst levels of other components remain substantially unaffected. The process of EP 0 280 817 involves traversing tobacco with a solvent in the supercritical state or liquid state. The solvent is then passed through an acid-containing trap where it is essentially freed of nicotine. The solvent, depleted of nicotine, but still enriched with the other components that have partitioned into the supercritical phase, is recycled back to the cellulosic component of the tobacco.
CN 1459256 discloses the use of supercritical CO2 extraction to remove harmful elements from tobacco. The supercritical CO2 containing tobacco rag extract is fed into rectifying separators which contain adsorbing materials, such as activated charcoal, under pressure and a controlled temperature, in order to remove harmful tobacco components. The supercritical CO2 is then brought back into contact with the tobacco rag and the temperature and pressure is lowered in order to effect transfer of the desired components back to the rag.
Means for isolating components from supercritical fluid are also known. For example, U.S. Pat. No. 6,637,438 discloses the use of high-pressure liquid chromatography (HPLC) to separate the fractions obtained by supercritical fluid extraction. However, methods of separation such as chromatography use solvents which are potentially toxic, environmentally unfriendly and/or flammable, and which are typically required to be removed from the components after isolation. Such solvents include benzene, cyclohexane, dimethylsulfoxide, acetonitrile, trifluoroacetic acid, triethylamine and methanol.
Furthermore, it can be very difficult to effectively isolate individual constituent components from a supercritical fluid. This is particularly the case where the desired component is present within the feed material in very small quantities, or when the property of the component by which it is isolated is very similar to that of other components found in the feed material. For example, chromatography techniques such as HPLC and gas chromatography rely upon differences in polarity between the samples to be separated. Gel filtration chromatography relies upon differences in molecular weight. It is therefore very difficult to isolate components which have a similar molecular weight or polarity using these techniques.
Another known method for separating a mixture of miscible liquids is distillation. Companies such as VTA Verfahrenstechnische Anlagen GmbH & Co. KG (Niederwinkling, Germany) have significant expertise in the field of distillation. Distillation is the process of heating a liquid until it boils, capturing and cooling the resultant hot vapours, and collecting the resultant condensed sample. It is possible to separate mixtures based on differences in the volatilities of components in a boiling liquid mixture using distillation. Idealized models of distillation are essentially governed by Raoult's law and Dalton's law.
Raoult's law assumes that a component contributes to the total vapor pressure of the mixture in proportion to its percentage of the mixture and its vapor pressure when pure.
Dalton's law states that that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture. When a liquid mixture is heated, the vapour pressure of each component within the mixture will rise, thus causing the total vapor pressure to rise. When the total vapor pressure reaches the pressure surrounding the liquid, boiling occurs and liquid turns to gas throughout the bulk of the liquid. A mixture with a given composition has one boiling point at a given pressure, when the components are mutually soluble.
At boiling point, all volatile components of the mixture boil, but the percentage of a single component in the vapour is the same as its percentage of the total vapour pressure. Lighter components have a higher partial pressure and thus are concentrated in the vapor, but heavier volatile components also have a partial pressure and necessarily evaporate also, albeit being less concentrated in the vapour.
Typically, distillation is carried out using a fractionation column. The mixture is heated until it vaporizes. The vapour passes up the fractionation column, where it is gradually cooled. Different components of the vapour condense at different levels within the fractionation column, allowing the (now liquid) components of the original mixture to be separated.
A disadvantage of a simple distillation procedure, wherein a single vaporization and condensation phase is used, is that it would not effectively separate a mixture whose boiling points differs by less than 60-70° C. Repeated fractionating cycles, to try to separate mixtures with more similar boiling points, can be expensive, and still not achieve the aim of providing a pure distillate of one of the substances in the mixture, particularly where the components have the same, or very similar boiling point.
For example, CN 1166 753 discloses the use of multi-stage molecular distillation process to separate tobacco components from an extractum which has been obtained by exposure of crushed tobacco pieces to petroleum ether in hot or cold conditions.
The difficulties in effectively isolating individual constituent components from an extract provided by supercritical extraction presents a particular problem when considering the isolation of components from tobacco which impart a flavour or aroma to the tobacco. This is because many such components are similar in nature, and have similar physical properties, to components of tobacco which are considered undesirable.
For example, it can be desirable to ensure that isolated components are not contaminated with nitrosamines. Nitrosamines are a class of chemical compounds which were first described in the chemical literature over 100 years ago. Tobacco is known to contain certain nitrosamines, which are known as tobacco-specific nitrosamines (TSNAs). TSNAs consist of four chemical compounds: N-nitrosonornicotine (NNN); 4-methyl-N-nitrosamino-1-(3-pyridyl)-1-butanone (NNK); N-nitrosoanatabine (NAT); and N-nitrosoanabasine (NAB). TSNAs are not thought to be present in any significant amount in growing tobacco plants or fresh cut tobacco (green tobacco), but are thought to be formed during the curing and aging of tobacco.
Another compound that it may be desirable to selectively remove from a tobacco extract is benzo[a]pyrene (Ba]P), a polycyclic hydrocarbon which is found in the environment, and in tobacco smoke.
It can undesirable for constituents of tobacco that are isolated in order to utilize their desirable flavour or aroma characteristics to be significantly contaminated with benzo[a]pyrene and/or TSNAs. Such contamination has the potential to happen using some methods of isolating compounds, as a result of the similarity of the physical properties of these compounds to those of the constituents of tobacco which it is desirable to isolate.
It can also be undesirable for the constituents of the cellulosic material that are isolated in order to utilize their flavour or aroma characteristics to be significantly contaminated with nicotine. For example, it may be desirable to use such constituents in a nicotine-free product. Contamination by nicotine has the potential to happen using some isolation methods, as a result of the similarity of the physical properties of nicotine to those of the constituents of the cellulosic feed material which it is desirable to isolate.
For example, nicotine has a molecular weight of 162.24 g, and the flavourant safrole has a molecular weight of 162.2 g. Use of a standard gel filtration separation procedure, which isolates compounds from a mixture on the basis of their molecular weight could not, therefore, be used to obtain a substantially pure sample of safrole from a supercritical fluid which has been contacted with a feed material that also contained nicotine.
Table 2, below, details some of the physical properties of aroma compounds which are typically found in tobacco. Table 2 also provides details of the some of the physical properties of components of tobacco which can be considered undesirable.
TABLE 2SolubilityFlavour/tasteBPtMPtMWt(g/100 mLDensityNamedescription(° C.)(° C.)(g/mol)water)(g/cm3)NNN—15347177.2NNK—71-73207.23NAT—189.21NAB—191.23B[a]P—495179252.31Insoluble1.24NicotineBitter247−79162.26Readily1.01solubleSolanoneTobacco smoke194.31BenzaldehydeAlmonds178.1−26106.120.61.0415PhenylHoney like/193−10120.15acetaldehydesweet/rose/grassyNonanalStrong fruity/195−18142.24Insoluble0.827floralCembreneFaint wax like150-152272.47LinaloolFloral with hint of198-199<20154.250.15890.86-0.87spicinessMethyl-Waxy with honey242.40.866tetradecanoateundertoneCoumarinVanilla30171146.140.935PulegoneMint, camphor224152.23Insoluble0.9346PiperonalFennel notes26435-37150.13trans-Anise/fennel23420-21148.20.998anetholeSafrole232-23411162.21.096MethylSpicy, woody,256−9164.21.06eugenolclove-likeMyristicinnutmeg173<25192.21.1437NNN: N-nitrosonornicotine;NNK: 4-methyl-N-nitrosamino-1-(3-pyridyl)-1-butanone;NAT: N-nitrosoanatabine;NAB: N-nitrosoanabasine;B[a]P: benzo[a]pyreneMwt: molecular weight;BPt: Boiling point;Mpt: Melting point
Contamination of one or more desired constituents with undesirable compounds results in the need to process the sample further. This can be costly and time-consuming.
JP 9-10502 discloses a procedure to extract an “objective component”, such as nicotine, from a natural solid raw material, involving bringing the raw material into contact with a first high pressure fluid. The fluid, and the components dissolved therein, are then brought into contact with an absorbent. The absorbent-soluble components are then brought into contact with a second high pressure fluid, which has been subjected to a temperature gradient. The temperature gradient ensures that only the objective components are dissolved in the second high pressure fluid. The second high pressure fluid containing the objective components is introduced into a separator where the objective component(s) are separated out by reducing the solubility of the objective component in the second high pressure fluid.
WO 2007/053096, which is concerned with the isolation and removal of nitrosamines from tobacco, discloses a method which requires more than 10 processing steps.
An object of the present invention is to provide a simple process which allows the selective isolation of components from cellulosic feed material.
In particular, it is an object of the invention to provide a simple process which allows the isolation of compounds which are similar in boiling point and/or vapour pressure.
A further object of the invention is to provide a process which comprises less than 5 processing steps.
It is a further object of the invention to provide a process which is relatively environmentally friendly, in that it does not require polluting separation matrices.
It is also an object of the invention to provide a process which does not require the use of a potentially toxic or flammable extraction solvent in order to extract soluble components from the cellulosic material; and which does not require the use of a solvent in order to isolate constituents from the extract.
A further object of the present invention is to provide a method which has a high degree of controllability in terms of the instruments and/or machinery that is commercially available to carry out the steps.
It is a further object of present the invention to provide a process which is relatively inexpensive.
A further object of the invention is to provide a process which is relatively clean, in that the machinery involved in the process does not require excessive cleaning cycles to be returned to original working order.